Expert: Ed - 7/18/2009

Question
I've seen pictures of lunar rilles, are they found only on the floor of lunar seas or do they intrude into the highlands
Thank you

Answer
Joseph,
They are usually in the maria, but not always.  The word "rille" usually refers to a collapsed lava tube, which, as a feature related to magma, are often found in the maria, because maria are also formed by magma.

"Straight rilles," as opposed to arcuate or sinuous rilles, are different phenomena.  If astronomers had to do it all over again, they would probably give a completely different name to straight "rilles," and not call them rilles at all.  They sometimes pass through the highlands.  This is because they are not collapsed lava tubes at all, but simply the division between lunar tectonic faultlines.
http://en.wikipedia.org/wiki/Rille

I hope this is helpful.  Keep Looking Up,
-Ed